This invention relates to a thrust support system for a vertical shaft rotary machine such as a vertical shaft hydraulic turbine generator or a vertical shaft pump, more particularly to a thrust support system for finally supporting on a stand the thrust of a rotator of a large machine.
In a large vertical shaft rotary machine, the weight of the rotator is large and hence load transmitted to the stand is greatly increased. For example, in a water turbine generator, a thrust bearing supports not only the rotator of the generator but also the weight of the rotary section of the turbine and hydraulic thrust of turbine. Hence, a load as large as several thousand tons should be frequently transmitted to the stand.
For this reason, the thrust support system for transmitting load to the stand is needed to be strong.
The thrust support system which has heretofore been adopted in general, as disclosed in U.S. Pat. No. 2,701,171 for example, has a bearing oil tank, provided at the center portion thereof with a throughhole for receiving a rotary shaft, and a plurality of spider arms extending horizontally and radially from said oil tank. The tail end of said arm is mounted on the stand, to thereby support the rotator. In general, said spider arm is of letter `I` shape in section. In many cases, the thrust of the rotator is controlled by bending strength of said spider arm and strength of the oil tank in displacement of the diametral direction.
However, in the case where the decrease in weight or improvement in strength is sought in designing a structure of machine, it is desirable to design the structure in which the members constituting the structure each carry uniform stress.
Additionally, it is desirable that the stresses generated in the members are in the conditions of simple tension stress or compressive stress as possible. The use of the members in the conditions of shearing stress is not advantageous because shearing modulus of elasticity is by far less than compression modulus of elasticity.
From the viewpoint described above, construction of the support system, i.e., bracket of the prior art has been such that load is supported by bending strength and shearing strength of spider arms and hence utilization rate of the material is low, and it is not expectable to considerably decrease the weight unless allowable stress is increased to an extreme extent. Since the increase in allowable stress results in the decrease in rigidity accordingly, distortion and vibration are increased, thereby possibly presenting new problems.
Further, the spider arm is of letter `I` shape in section, and constructed by being welded substantially on all the periphery. However, it has been extremely troublesome to carry out such a welding work and inspection in a narrow space within the stand.